I really like this website: http://womensfashion.suite101.com/article.cfm/color_coordinating_clothes. It gives you a list of "main" colors, and then good colors to go along with that. So, if you know you want to wear your favorite dark brown shirt, you can look at the list of colors that coordinate well with that color. In the case of dark brown it suggests lemon yellow, baby blue, mint green, baby purple, or lime green. Don't feel like your restricted to these colors either, but it's a good start if you're feeling lost in color decisions.
They also talk about color combination's to avoid:
"It’s best to avoid holiday colors such as red and green, orange and black, pink and red, along with red and yellow, which bring to mind the hamburger chain with golden arches. Steer away from wearing the same color on top and bottom unless it’s black. For instance, a red shirt with red pants can look tasteless and tacky."
For family photos, I like to see people wearing things they're comfortable wearing, and that you would see them wear out and about. Make sure you like it and have fun with it. Don't stress about it! And don't feel like you need to follow the exact guidelines of the "experts". I like bright colors and fun things. If you're really struggling with ideas, look at other family photos that you like, and pull ideas from there. And always always be comfortable and have fun!
I'll end on a photo of a nicely color coordinated family :)
